Under the Data Over Cable Service Interface Specification (DOCSIS) standard, a Layer 3 forwarding Cable Modem Termination System (L3 CMTS) manages the access to a plurality of subscriber cable modems and devices connected to the cable modems. Each cable modem (CM) and devices behind it get an Internet Protocol (IP) address through the L3 CMTS. These IP addresses normally belong to IP subnets which are possessed by the L3 CMTS. Thus the L3 CMTS is configured with a plurality of IP subnets, and is in charge of the access to all the devices in these subnets.
An external server has a need to dynamically create a flow to a subscriber (e.g., voice calls, video sessions). The server needs to establish quality of service (QoS) parameters for this flow to guarantee that the service is properly delivered over the DOCSIS shared access domain to the subscriber. In another example, a different server requires tapping data traffic to a specific subscriber for purpose of Lawful Intercept (LI). In both cases the server has to communicate/negotiate with the entity in charge of the access to that subscriber: the L3 CMTS. The server has to find out which of the plurality of L3 CMTS units in belonging to the service provider (Cable operator) is in charge of the access to the particular subscriber associated with the flow/LI.
Rather than inquiring with every possible L3 CMTS each time that a new dynamic session is needed, the server maintains a database of the IP subnet scope handled by all L3 CMTS units, searches for the IP address of the particular subscriber in that database, and identifies the L3 CMTS in charge of access to that subscriber. Since the service provider may occasionally change the subnets handled by each L3 CMTS, the server has to update that database periodically. Thus, the server can periodically query each and every L3 CMTS for the subnet scopes that they handle, and each L3 CMTS units provide its subnet scope information according to the configuration it received.
Alternative methods exist to query a L3 CMTS for its IP subnets scopes. Example for such methods is SNMP, which requires a-priori knowledge of the L3 CMTS own IP address. A second example is the Control Point Discovery protocol (CPD) specified by Cablelabs, which does not require a priori knowledge of the L3 CMTS own IP address but also enable a server to query a L3 CMTS for its IP subnets scopes.
A layer 2 forwarding CMTS (L2 CMTS) is also permitted under the DOCSIS spec. Such L2 CMTS works in conjunction with an Edge Router (ER) to provide equivalent service to a L3 CMTS. In such a case, the configuration of the IP subnets the L2 CMTS is in charge of access to is provided to the ER and not to the L2 CMTS. Although the configuration can be provided to both devices, it is highly desired not to duplicate redundant configuration since it requires more operations and may results in errors. There exists a problem where the L2 CMTS needs to obtain the subnet information for the DOCSIS shared domain it controls the access to, so that information can be communicated to external servers requiring it. While the ER has this information, it is not the access control point and cannot be communicated with in order to establish dynamic flows.